The circulatory system of fish.

Fish have a circulatory system. They are cold-blooded because their bodies cannot maintain a certain temperature. Fish have only one circle of blood circulation. The heart of a fish consists of two chambers – the atrium and the ventricle. This is enough, since no more chambers are needed for one circle of blood circulation. The vessels pass through the gills, where carbon dioxide is exchanged for oxygen. The blood in the body cavity of the fish body does not enter during the blood circulation, which means that the fish have a closed circulatory system.